The present invention concerns a printing unit for printing with flexographic inks and lacquer in an offset printing machine that includes a printing plate cylinder, a rubber sheet cylinder, a back-pressure cylinder and an inking unit which includes a screen roller in engagement with a doctor blade system and which is arranged for continuous rotation, either by engaging a motor in a situation where the printing machine is not operating or by engaging the transmission of the printing machine when the printing machine is operating, the screen roller being arranged for swinging in and out of engagement with rubber sheet cylinder which has an axially oriented channel limited by the front edge and the rear edge of the rubber sheet.
The invention further concerns a printing machine with such a printing unit and a tool for use in mounting and dismounting the washing facility and the inking unit in such a printing machine.
The invention furthermore concerns a method of operation for printing with flexographic inks and lacquer in an offset printing machine which includes a printing plate cylinder, a rubber sheet cylinder, a back-pressure cylinder and an inking unit which includes a screen roller engaging a doctor blade system and which is continuously rotated, either by engaging a motor in a situation where the printing machine is not operating or by engaging the transmission of the printing machine when the printing machine is operating, the screen roller being arranged for swinging in and out of engagement with rubber sheet cylinder which has an axially oriented channel limited by the front edge and the rear edge of the rubber sheet
It is prior art to produce printing machines in which are placed different printing units, so that an offset printing machine also can be used with flexographic inks and lacquer. Examples of such prior art machines of the kind mentioned in the introduction are found e.g. in PCT/DK98/000303 and in EP 1 093 913.
The reason of the present invention is a need for providing a modular system, where a washing facility for the rubber sheet cylinder in a printing unit readily may be substituted with an inking unit, and where there is no risk that ink in the screen roller of the inking unit dries up simultaneously with enabling driving the inking unit by the transmission found in the printing machine in order to provide an operation of the printing unit which is entirely synchronous with the number of revolutions of the rubber sheet.
When the printing unit is of the type with screen roller engaging a doctor blade system, problems will arise with drying of ink/lacquer in the screen roller when the printing machine is standing still or when the screen roller is brought out of engagement with the rubber sheet cylinder, as the screen roller is not rotating in these situations.
When changing the printing machine by shifting between the washing facility and the inking unit, it is important that this occurs very quickly for reducing the down-time of the machine. By the known machines it is furthermore an ergonomically inconvenient task to perform substitution, since washing facilities usually are positioned obliquely under the rubber sheet cylinder. Therefore, it is difficult for an operator to get a real hold on the washing facility/inking unit. This also implies risk of the washing facility/printing unit falling down and causing damage of parts in printing machine and/or the washing facility/inking unit.